Abstract

A fluoroquinolone-resistant Escherichia coli strain of sequence type ST131 caused severe septic arthritis and contiguous osteomyelitis in an 8-month-old girl, and colonized the girl's healthy mother, who shared a different fecal E. coli strain with the father. Within-household transmission can contribute to the dissemination of the emerging, multidrug-resistant ST131 clonal group, which has evident invasive potential for otherwise-healthy children.